Switch actuating mechanism for controlled speed tap changer



Nov. 3, 1964 e. A. WILSON, JR

SWITCH ACTUATING MECHANISM FOR CONTROLLED SPEED TAP CHANGER 4Sheets-Sheet 1 Filed May 1, 1959 .INVENTOR. Gordan fl. 21425072 (/3: BYi F SWITCH ACTUATING MECHANISM FOR CONTROLLED SPEED TAP CHANGER 4Sheets-Sheet 2 Filed May 1, 1959 12b 74 7&

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Nov. 3, 1964 G. A. WILSON, JR

SWITCH ACTUATING MECHANISM FOR CONTROLLED SPEED TAP CHANGER 4Sheets-Sheet 3 Filed May 1, 1959 Vac u mxQm m EB Q ms Em Geneva PinionDisplacement r J n w NZ WM/ m TM Z a m Y B fittormy Nov. 3, 1964 e. A.WILSON, JR 3,155,782

swITcl-x ACTUATING MECHANISM FOR CONTROLLED SPEED TAP CHANGER 4Sheets-Sheet 4 Filed May 1, 1959 INVENTOR 60721072 #4. M'Zson d3".

fit tarney United States Patent SWHCH AQTUATENG MECHANHSM Fill; ECQN-TRQLILED SPEED TAP CHANGER Gordon A. Wilson, l ra, Washington, Pa,assimior to itic'Graw Edison (iompany, Milwaukee, Win, a corporation ofDelaware Filed May l, 1959, tier. No. 81%489 21 Claims. till. Edd-12)This invention relates to switching mechanisms and more particularly totap changers for stationary induction apparatus.

A tap changer is often utilized to accomplish voltage regulation ofstationary induction apparatus. Usually the tap changing mechanism isoperated under load while the stationary induction apparatus iselectrically energized, and the contact movement should therefore be ata relatively high speed to minimize contact erosion. l-ieretofore it hasbeen conventional to utilize a drive mechanism in the tap changerincorporating a resilient energy storage means that actuates the movablecontact with a snap action. Such spring-drive mechanisms are notentirely satisfactory in that they do not positively control the speedof contact movement but act only as initiators of motion. The movablecontact is not disengaged from the preceding stationary contact withoptimum speed to insure minimum contact erosion, and the movable contactis brought into en agement with the succeeding stationary contact atmaximum velocity with the result that contact bounce occurs drawingrepeated arcs between movable and stationary contact until the movablecontact finally comes to rest. As a consequence contact life isrelatively short and the mechanical shock, vibration, and unbalancedinertial forces accompanying the snap action necessitate frequentservicing and maintenance of the tap changer and result in shortmechanical life thereof. Further, conventional load tap changingequipment utilizing resilient stored-energy drive means is unnecessarilybulky and heavy.

it is an object of the invention to provide a direct-drive tap changingmechanism which positively controls the speed of switching and thusinsures maximum contact life.

Another object of the invention is to provide an improved tap changerwhich positively indexes the movable contacts from one stationarycontact to a succeeding stationary contact and inherently insurespositive mechanical interlocking of the movable contacts.

Still another object of the invention is to provide a tap changingmechanism in which the movable contact starts slowly and is thereafterrapidly accelerated to optimum velocity for eiiicient are interruptionas the contacts open.

A still further object of the invention is to provide a tap changer inwhich the movable contact is not snapped at maximum velocity intoengagement with a succeeding stationary contact but rather isdecelerated to a fraction of its maximum velocity before the contactsclose.

it is a further object of the invention to provide a tap changingmechanism which decelerates the movable contact to a fraction of itsmaximum velocity before the movable contact engages a succeedingstationary contact and positively constrains the movable contact as itis slowed down and until it is brought to rest in engagement with saidsucceeding stationary contact, whereby contact bounce is eliminated andmechanical shock and vibration are minimized.

A still further object of the invention is to provide a switchingmechanism which gradually accelerates the movable contact during theinitial portion of the indexing thereof, which rapidly accelerates themovable contact to optimum velocity for efficient interruption beforethe contacts open but provides gradual change of velocity over asubstantial portion of the velocity-time characteristic on both sides ofthe maximum velocity point where slowing down of the contact begins, andwhich gradually decelerates the movable contact during the final portionof the motion as the movable contact approaches its final position atrest with a succeeding stationary contact, whereby switching action issmooth and shock, unbalanced inertial forces, and vibrational effectsare minirnized.

Still another object of the invention is to provide a tap changingmechanism wherein the slope of the midportion of the velocity-timecharacteristic of the movable contact chan es gradually from plus onethrough zero to minus one, whereby inertial forces are minimized in theindexing of the movable contact.

Another object of the invention is to provide a tap changing mechanismwhich alternately indexes a pair of movable contacts and is adapted tolock one movable contact at rest while simultaneously actuating theother movable contact and to positively control the speed of said othermovable contact while indexing it into engage- 1611i with a succeedingstationary contact. A further object is to provide such a tap changingmechanism having novel means for positively indexing and controllingcontact speed including a rotatable index plate carrying a plurality ofcam followers and a positive-motion cam adapted to sequentially engageand peripherally displace the cam followers. A still further object isto provide such a tap changing mechanism wherein the cam is rotatablydriven in a series of steps to index a movable contact betweenstationary contacts and is adapted to positively engage a cam followerand displace it in the first step before the contacts open to a positionmost advantageous for rapid acceleration of the movable contact duringthe succeeding step, to start the cam follower slowly and thenaccelerate it rapidly during contact interruption and decelerate the camfollower while positively constraining it to close the contacts slowlyand prevent contact bounce during the second step, to positively remainin engagement with the cam follower during the third step until the camengages a succeeding cam follower, and also to positively lock themovable contact at rest.

Still another object of the invention is to provide an improved tapchanging mechanism wherein the gradual acceleration and deceleration atthe ends of the motion transmitted by an intermittent motion device aresuperimposed upon the motion of a cam having gradual change of velocitynear the midportion of the velocity-time characteristic to providesmooth action of the rotatable contact and which also permits the primemover to start without load.

A further object of the invention is to provide a load tap changingmechanism that is substantially smaller in size and lighter in weightthan conventional spring-drive tap changing mechanisms.

Another object of the invention is to provide a load tap changingmechanism that is much simpler in construction and much more rugged thanprior art springdrive load tap changing units.

A specific object of the invention is to provide a tap changer whereinthe intermittent motion of a Geneva gear is superimposed upon that of asimple harmonic motion cam to index the movable contact and providesmooth action thereof.

These and other objects and advantages of the invention will be moreapparent from the following detailed description when read inconjunction with the accompanying drawing in which:

FIG. 1 is a front view of a preferred embodiment of the invention withthe drive mechanism of one phase broken away to illustrate the contacts;

FIG. 2 is a cross sectional view taken on line 2-2 of FIG. 1;

FIG. 3 is a development of a cylindrical cam utilized in the embodimentof FIG. 1;

FIG. 4 is the velocity-time characteristic of the movable contact of theembodiment of FIG. 1;

FIG. 5 is a perspective view of the novel means for positively indexingthe movable contacts from one stationary contact to a succeedingstationary contact; and

FIGS. 6-10 schematically illustrate sequential positions of the cam andindex plates of the direct-drive means at different steps of a tapchange.

The underload tap changing mechanism of the invention Will be describedas incorporated in a three phase load tap changing transformer. The tapchangers 1b of all three phases are identical and only one will bedescribed. The tap changers it? for all three phases are enclosed withinan oil-filled compartment (not shown) on the sidewall of the maintransformer tank which houses the three phase transformer core and coilassembly. The tap changers id for all three phases are mounted on aninsulating panel ill preferably of low power factor, low loss dielectricmaterial which forms an oil-tight barrier between the main transformertank and the oil-filled compartment.

A plurality of arcua'tely positioned stationary contacts 12 mounted onpanel ll-ll include a first coplanar set of nine metallic stationarycontact members 12a disposed in a circle and spacedfrom a secondcoplanar set of nine metallic stationary contact members 12]) arrangedin a circle. Corresponding stationary contact members 12a and 12b of thetwo sets are electrically comnroned. The corresponding contact members12 a and 12b of each stationary contact 12 have clearance holes forreceiving threaded metallic studs 14 and are spaced apart by tubularmetallic members 15 surrounding the studs M. The studs M threadablyengage a metallic contact supporting member 16 which is rigidly securedto a threaded metallic pin 1% extending through panel 311. An insulatingcollar 19 surrounds pin 18 between member 16 and panel ill, a nutthreaded onto pin 18 on the side of panel 11 Within the transformer tankfixedly mounts contact supporting member 16 and stationary contact 12 oninsulating panel ill. The insulating collar 19 mounts stationary contact12 on an insulating projection away from the insulating barrier providedby the panel 11 between the transformer and the tap changingswitch lit,and this construction transfers the dielectric stress from theinsulating barrier to the oil and permits reduction in the size of thetap changing apparatus. A nut threadably engaging stud M rigidly clampsmetallic stationary contact member 12!) against the metdlic sleeve 15and also rigidly clamps the stationary contact member 12:: betweencontact support member To and tubular support 15.

Electrical leads 21 connect eight of the stationary contacts 12toindividual taps (not shown) in the tapped series winding of thecorresponding phase of the transformer, and a lead 22 electricallyconnects the ninth, or neutral contact 23 to the main Winding.

Three insulating panel boards 25 within the oil-filled compartment, oneassociated with each of the phases, are mounted in spaced relation tothe panel 11 by electrically conductive support studs are surrounded byinsulating sleeves 27. Each sleeve 27 is positioned between panel illand a metallic member 3t secured by suitable means such as brazingadjacent one end of a stud 26. A tubular insulating member 24 surroundsthe end of each support stud 26 within the transformer tank, and nutsthreadably engaging the ends of studs 26 clamp the panel 11 against oneend of the insulating sleeves 27 and panel board 25 against the members3% to mount panel boards 2-5 in spaced relation to panel llll.

A rotatable shaft 28 carrying a movable contact 29 adapted tosequentially engage the stationary contact members 12a extends throughan opening in the panel board 25 with its axis coincident with thecenter of the circumferentially arranged stationary contact membersllZa. One end of shaft 2?} is journalled in a mounting bracket 33secured by bolts 34 to panel board 25. A bifurcated switch arm 36affixed by suitable means such as rivets to a radially extending flange3! on shaft 28 carries the rotatable electrical contact 29. Rotatablecontact 29 includes a pair of opposed, generally radially extending,laminated copper shunts 39. Each copper shunt 39 has a contact button 41at the radially inward end thereof and an arcing contact button 42 atthe radially outward end thereof. Rear swivel plates 31 and front swivelplates 32 positioned against the radially inward and radially outwardportions respectively of each shunt 3% have inwardly formed portions(not shown) pivotally connected together by swivel pins 43 which extendthrough a thrust piece 47. Thrust piece 2'? has circumferentiallyextending portions secured by bolts 4% to the arms of bifurcated switcharm 36. The arcing contact buttons 42 are opposed and urged together bycompression springs 44 surrounding pins 45 protruding through clearanceholes in the copper shunts C19 and in the front swivel plates 32 andcompressed between heads 46 on the ends of the pins 45 and the frontswivel plates 32. Similarly the radially inward contact buttons 4-1 areopposed and urged together by compression springs 44 surrounding pins d5projecting through clearance holes in the copper shunts 3-; and in therear swivel plates 31. The springs id resiliently urge arcuate portionsof laminated copper shunts 39 against thrust piece 47 and also urge thearcing contact buttons against opposite sides of stationary contactmembers The contact buttons 41 at the radially inward end of shunts 39are resiliently urged by the helical springs dd against a collector ring49 formed by the circumferential flange on a conical member 5%) of asuitable metallic material. The collector ring flange 49 is coplanarwith the stationary contact members 12a, and the conical metallic member5d is rigidly secured to a metallic support member 51 which is disposedagainst panel fill and, in turn, is affixed to a metallic stud 52 whichextends through insulating panel 11. A nut 53 threadably engaging theend of stud 52 within the transformer tank fixedly mounts conical memberit} on insulating panel Ill, and the end of metallic stud :52 within thetransformer tank is connected by a lead to one end of a preventiveautotransformer (not shown) enclosed within the transformer tank.

A sleeve 55 rotatably surrounding the shaft carries a rotatable contactas identical to rotatable contact 29 and adapted to sequentially engagethe stationary contact members 12b. The sleeve 55 is journalled within atubular portion 57 of support casting A bifurcated switch arm identicalto switch arm '36 is secured by suitable means such as rivets to aradially extending flange on sleeve 55, and switch arm 5: carries therotatable contact Rotatable contact as carried by sleeve 55 is adaptedto sequentially engage stationary contact members 12b and toelectrically connect them to a collector ring formed by acircumferential flange (all on a conical member 62 of a suitablemetallic material. The circumferential flange at is in the plane of thestationary contact members 1212, and the conical metallic member as isrigidly affixed to a metallic support member as surrounding sleeve 55and fixedly mounted on a copper strap Copper strap 64- is rigidlysecured to insulating panel board 25 by bolts which mount bracket 33.Copper strap 64 extends along the surface of insulating panel board 25.The lowor end of copper strap 64- is bent beneath the lower edge ofpanel board 25 and is electrically connected to a support stud 2s. Theend of conductive support stud as within the transformer tank iselectrically connected by a lead 65 to the other end of the preventiveautotransformer (not shown).

Shaft 28 and sleeve 5'5 are actuated independently in a manner to bedescribed later so that rotatable contacts 29 and 55 are individuallyoperable. Inasmuch as stationary contact members 12a engaged byrotatable contact 29 and stationary contact members 1211 engaged byrotatable contact 56 are electrically commoned, the rotatable contacts29 and 56 can be indexed to a bridging position wherein each of therotatable contacts 29 and 55 is on one of two adjacent stationarycontacts 12 and the voltage obtained is midway between the taps, or to asymmetrical position wherein both movable contacts 29 and 56 are on thesame stationary contact 12. A tap changer 1th and associated serieswinding provide plus or minus ten percent voltage regulation, andinasmuch as eight stationary contacts 12 are electrically connected toeight taps in the series winding, a 1% percent variation in voltageoccurs when both rotatable contacts 29 and 56 are indexed to asucceeding stationary contact. Movement of only one rotatable contact 29or 56 to a succeeding stationary contact l2 results in a voltage midwaybetween the taps, or /8 percent regulation, and full plus or minus 10percent voltage regulation is accomplished in thirty-two percent steps.

A reversing switch 67 includes a U-shaped metallic contact 68 atlixed tothe metallic stud 14- of neutral stationary contact 23 and extendingthrough an aperture 69 in panel board 25 and also includes a movableelectrical contact '74). The stationary contact 63 has a circumferentially elongated arcuate portion '71, and movable contact ill isadapted to electrically bridge between arcuate portion 71 and reversingswitch stationary contact members 72 and 73. Each stationary contact 72and '73 is secured by bolts '75 surrounded by insulating sleeves 76threadably engaged within tapped holes in a metallic member 39 disposedadjacent the transformer side of panel board 25. As describedhereinbefore member 3b is rigidly secured to a conductive support stud25. The stationary contact members 712 and 73 of the reversing switch 67are each electrically connected through the support studs 26 toelectrical leads 79 which are connected to opposite ends of the tappedseries winding Within the transformer tank.

When tap changer it? has both movable contacts 29 and 5s on neutralcontact 23, and thus the reversing switch 67 is out of the load circuit,an axially extending driving pin carried by a reversing link Sll affixedto and rotatable with the sleeve 55 is adapted to engage on open-endslot 82 at the lower end of a pivoted switch arm 85 carrying the movablecontact 7th to pivot the switch arm 84- and thus disengage the movablecontact 7d from one stationary contact 72 or 73 and actuate it intoengagement with the other stationary contact. Switch arm 84 includes alocking member 37 in which open-end slot 82 is formed and a bifurcatedinsulating member $8 carrying movable contact 7@ and secured to lockingmember 37 by suitable means such as rivets. A pin 9% extending throughmembers 87 and 88 is journalled within a sleeve portion 91 of supportbracket casting 33 to pivotally mount the reversing switch 67. Thereversing switch 6? changes the connections to the tapped series windingfrom lower to raise and vice versa and thus doubles the voltage range ofthe tap changer. The reversing switch s7 is only actuated when bothmovable tap changer contacts 2% and 56 are engaging the neutral contact23.

Although the electrical elements are not shown, the electrical circuitof the load tap changing transformer may be traced through a tap changerill from the transformer secondary phase winding through the lead 22;the neutral contact 23; U-shaped stationary contact as of the reversingswitch 67; reversing switch movable contact lii to either stationarycontact strip '72 or '73; through a support stud 2d and a lead 79 to oneend of the series winding within the transformer tank; a portion of theseries winding; a tap in the series winding; a lead Zll to a stationarycontact 12; movable contacts 29 and 56 (assuming both are on the samestationary contact); collector rings 4-9 and 61 to the preventiveautotransformer;

(5 and from the midtap of the preventive autotransformer to the load.

A circular index plate $2 is fixed to the end of the shaft 2ft,preferably by a splined connection, to provide a positive andnonresilient connection with rotatable contact index plate 92 carriesnine equiangularly spaced apart cam follower rollers 93 fixed thereto bybolts 94. A second index plate 95 coaxial with plate 92 and axiallyspaced therefrom is connected to the sleeve 55, preferably by a splinedconnection. The index plate 95 is also provided with nine equiangularlyspaced apart cam follower rollers $6 fixed thereto by bolts 7. Apositivemotion cylindrical cam 99 disposed between index plates 92 and$5 is fixed, preferably by a splined connection, to a horizontallyextending shaft ltll the ends of which are journallcd within spacedapart portions 1432 of support casing 33. The direct-drive means of theinvention for indexing the movable contacts between stationary contactsincludes the cam and the index plates 92 and E 5 alternately driventhereby.

The tap changer lift of each of the three phases of the load tapchanging transformer includes a cylindrical cam 99 splined to a shaftMil, and the shafts 191 of the three tap changers are connected bycouplings 1433 so that the three cams are rotatably drivensimultaneously. The cylindrical cam 99 of each tap changer llll isdisposed between the index plates 9?. and 95 with its axis at rightangles to and spaced below the axis of the index plates 92 and 95. Asshown in FIG. 5, the cam followers 93 and 96 are disposed on thesurfaces of the index plates 92 and $5 which face each other, and thecam followers of each index plate )2 and d5 are adapted to besequentially engaged and peripherally displaced by the cam 99 and alsothe cam followers 93 and 96 of each pair of index plates are adapted tobe alternately engaged and tangentially displaced by cam 3?.

The indexing means of the invention includes two relatively rotatablemembers one of which has a single means in continuous positiveengagement with the other member, and in the preferred embodiment suchsingle means includes a raised, axially advancing, camming surface means165 extending circumferentially more than 360 degrees around theperipheral surface of the cylindrical, or drum, cam 99. The peripherallylongest portion 167 of camming surface means M5, which in the preferredembodiment encompasses approximately 260 degrees of the circumference,is preferably in a plane substantially at right angles to the axis ofthe cam 9% and intermediate the camming surface end portions 199 andfill which overlap and diverge on opposite sides of said plane. Endportions lid? and fill extend over approximately 100 degrees of thecircumference and advance in a generally axial direction along thecylindrical surface of drum cam 99 and terminate at the opposite edgesthereof. The end portions 169 and 111 are similar and the inner facesthereof are complementary and define a double-edge, approximatelyS-shaped cam track portion 117 of the carnming surface means Edd. In thepreferred embodiment the cam track portion 117 is adapted to impartsimple harmonic motion to a cam follower 93 or 90. The cam 99 isreversible and can be driven in either a clockwise or counterclockwisedirection to peripherally displace the cam followers 93 and 9d.

The camming surface means alternately engages the cam followers 93 andMS of the pair of index plates 92 and 95. When cylindrical cam 99 isrotated, the midportion 107 remains in a plane radially of the indexplates 2 and 95 and thus applies no force tending to displace camfollowers 93 and 95. However, the approximately S-shaped double-edge camtrack portion 117 advances tangentially with respect to the index plates92 and 5 and thus circumferentially displaces the cam followers 93 and95 to cause rotation of index plates @2 and 95'.

As one cam follower, e.g. 93, on index plate 92 is being tangentiallydisplaced by approximately S-shaped doua B ble-edge cam track portion117 to index movable contact 29 to a succeeding stationary contact 12,the midportion N7 of camming surface means M95 is disposed between twocam followers 96 on the other index plate to lock the rotatable contactat rest While the index plate and associated rotatable contact 29 isbeing indexed from one stationary contact 12 to a succeeding one. Thedoubleedge cam track portion 117 positively constrains a cam follower 93while tangentially displacing it in order to provide a direct andnonresilient connection between cam 99 and index plate 92. Concurrentlythe midportion of camming surface means res is disposed between two camfollowers 96 of the index plate to provide a direct and nonresilientconnection between index plate 95 and cam 99 and thus lock rotatablecontact 56 at rest. it will thus be appreciated that direct andnonresilient indexing of the movable contacts 29 and as is accomplishedthrough cylindrical, or scroll, cam and index plates and 95 whichinherently insures positive mechanical interlocking of the rotatablecontacts 2% and 5d.

The direct drive of the rotatable contacts through the cam 99 results inpositively controlled contact speed which insures the most efficient arcinterruption. As explained hereinafter, the movable contacts 29 andstart slowly and are accelerated rapidly to the optimum s d for areinterruption before the contacts open. instead of being snapped atmaximum velocity into engagement with the succeeding stationary contactin the manner of the prior art spring-drive tap changers, the rotatablecontacts 23 and 5d are decelerated to a fraction of their maximumvelocity before engaging the succeeding stationary contact 12 and arepositively constrained by the direct and nonresilient connection betweencam and the cam followers 93 and 96 in order to close the contactsgently without contact bounce and with minimum mechanical shock andvibration. The control of contact speed is obtained through thecoordination of the cam 99 and the gear train which rotatably drives cam99.

The motive force for scroll cam 99 is derived from a reversible electricmotor 119 which drives the coupled shafts 1M through intermittent motionmeans preferably including a Geneva stop and pinion 121 rotatably drivenby the electric motor fill and a Geneva gear 123 actuated by the Genevapinion 1211. The intermittent motion eans is operatively connected tothe cams @9 of all three phases through a vertical operating shaft 125connected to the Geneva gear 123, and a pair of miter cars 1227 one ofwhich is afilxed to shaft 125 and the other of which is secured to anextension 123 on the shaft lltli of middle tap changer lit.

in the embodiment of the invention illustrated in the drawing, threesteps of the Geneva gear 12? produce 186 degree rotation of thecylindrical cam to positively index one of the rotatable contacts, e.g.,29, from one stationary contact 12 to a succeeding stationary contact12. The combination of cylindrical cam and Geneva gear 123 permits theelectric motor 11) to start without load during each step of cam $9.

The movement of the cam followers of one index plate, e.g., 92, relativeto the cam 99 is schematically illustrated in FIG. 3 wherein it isrepresented that prior to the tap change, two cam followers 93A and 93Bare disposed on opposite sides of midportion 97. The "rst step of wag ee11 Geneva gear 123 during the tap change rotates cam 99 sixty degrees sothat the initial, gradually sloping portion of double-edge,approximately s-shaped, cam track portion 117 positively engages one camfollower and effects minimum peripheral displacement thereof to aposition 933. At this position the tap changer contacts have not openedand the cam follower is at the beginning of the steeper-sloped portionof cam track llfi which is the most advantageous position to effectrapid opening of the contacts during the second step. Geneva gear 12.?then rotates cam 99 through another sixty degree step to displace thecam follower along the steepest-slope portion of double-edge cam track117 to a position denoted 933". Eur-- ing the second step of Geneva gear123, the cam follower is tangentially displaced from position $3B toposition 933" to rotate plate 92, and thus index rotatable contact fromone stationary contact 12 to a succeeding stationa y contact 12. At theend of the second step, the cam follower 938 at position 935 is stillpositively engaged by double-edge cam track portion E17 but cam follower93A at position %A" is disengaged from camr ing surface means The thirdstep of Geneva gear "5 rotates cam 99 through another sixty degrees todisplace cam follower 933 along the gradually sloping final portion ofdouble-edge cam track portion 117 to a position denoted 93B. It will benoted that only a minimal tangential displacement of the cam followeroccurs in moving from position 93B to the final position 9313" whereinthe contacts are at rest and also that in this final position the camfollower 93B and a succeeding cam follower 93C are disposed on oppositesides of the midportion iii? of camming surface means to thus lockrotatable contact 29 at rest while cam 99 is peripherally displacing acam follower 96 to index rotatable contact 56 into engagement with asucceeding stationary contact.

Although the camming surface means 1% is shown as a raised portion oncam 99, it will be apparent that the carnming surface means 1% canequally well be a groove in the surface of cam 99.

As mentioned hereinbefore, the camming portion I117 is the preferredembodiment of the invention is adapted to impart simple harmonic motionto the cam followers and During the first sixty degree step of simpleharmonic motion, a cam follower 93 or 96 is displaced along therelatively flat, gradually sloped portion of the camming surface means1635 to position the cam follower 93 or 96 at the beginning of themiddle, steeper-sloped portion of the simple harmonic motion cammingtrack ll? which is advantageous for rapid opening of the contacts duringthe second step of cam 99. During the second sixty degree step of simpleharmonic motion, the movable contact 29 or 55 is accelerated to anoptimum velocity for et'licient arc interruption before the contactsopen, is further accelerated to a maximum velocity, and is thendecelerated to a fraction of the maximum velocity before engaging thesucceeding stationary contact 12. Simple harmonic motion has the highlydesirable characteristic that the change in velocity occurs gradually atthe midportion of the velocity-time characteristic where the velocity isa maximum. Consequently, mechanical shock, inertial force, and vibrationare a minimum when t movable contact is being slowed down at themidportion of the velocity-time characteristic.

The intermittent motion of a Geneva gear has the desirablecharacteristic that acceleration and deceleration are a minimum at theinitial and final portions of the motion respectively, but thetime-velocity characteristic of a Geneva gear is similar to asharply-pointed inverte ii where change of velocity is a maximum on bothsides of the midportion thereof and consequently severe vibratoryeffects, inertial force, and mechanical shock occur at the midportion ofthe travel.

in accordance with the invention, the midportion of the simple harmonicmotion of earn 9, characterized by gradual change in veloc issuperimposed upon the "J 7 'y-time characteristic of the intermittentmotion device .9, characterized by gradual acceleration and decelerationat the ends of the motion, to obtain smooth action. of rotatablecontacts 29 and 56 with minimum unbalanced forces and vibration effectsduring the second step of cam 9% then the rotatable contact is beinginfrom one stationary contact to a succeeding stationary contact. Theresultant time-velocity characteristic of the rotatable contacts 29 and56 during the second step of cam is illustrated in FlG. 4 whereinvelocity of the rotatable contact is plotted against degrees rotation ofthe Geneva pinion 1251. it will be noted that the tremendousacceleration and deceleration at the ends of the motion characteristicof simple harmonic motion, or of constant acceleration motion, areabsent and that motion of the rotatable contacts 29 and 56 is initiatedslowly with gradual acceleration and is also slowed with gradualdeceleration at the final portion of the motion to bring the rotatablecontacts gently at rest in engagement with a succeeding stationarycontact. During the second step the rotatable contacts 2? and 56 arerapidly accelerated to almost half of their maximum velocity and to anoptimum speed for efficient arc interruption before the contacts open asindicated at point on the velocity-time characteristic of FIG. 4. Itwill be noted that the midportion of the velocity-time characteristicillustrated in FIG. 4 is approximately sinusoidal in contrast to theinverted-V characteristic of an intermittent motion device. Theacceleration, indicated by the slope of the velocitytime characteristic,diminishes gradually as the velocity of the rotatable contact approachesa maximum at the midpoint of the characteristic and further the changeof velocity occurs gradually as slowing down of the contact is begun.The slope of the rnidportion of the velocitytime characteristic of therotatable contacts 2% and 56 changes gradually from plus one adjacentpoint X through zero at the maximum velocity point and to minus oneadjacent point Y. Consequently, the action of the rotatable contacts 29and 56 is smooth, and the unbalanced inertial forces and severe shockand vibratory effects inherent in the inverted-V velocity-timecharacteristic of a Geneva gear drive are avoided.

During the final portion of the second step, the movable contact 29 orse is decelerated to less than half its maximum velocity before themovable contact engages the succeeding stationary contact as indicatedat C in FIG. 4, and the rotatable contact is positively constrained bythe direct and nonresilient connection between cam track portion 117 andthe cam follower 93 or 96 as the contact is gradually brought to rest atthe end of the motion in engagement with a succeeding stationary contact12. Contact bounce is thus entirely eliminated, no pitting of thecontacts occurs due to the drawing of repeated arcs during contactbounce as in prior art spring-drive tap changers, and electrical life ofthe tap changer contacts is greatly increased in comparison to prior artmechanisms. The minimum vibration, minimum unbalanced forces, andminimum mechanical shock inherent in the direct, positive andnonresilient indexing of contacts results in a much more ruggedmechanism which requires greatly reduced maintenance in comparison toprior art devices and has considerably greater mechanical life.

During the third step of cam 99, the cam follower 93B is moved along therelatively flat, gradually-sloped final sixty degree portion of thesimple harmonic motion camming surface means N35 to a position indicatedat 938'. The rotatable contact 2-9 is slowly brought into its finalposition at rest in engagement with the succeeding contact 12 during thethird step, and it will be noted that cam track portion 117 isdisengaged from cam follower 933 at the end of the third step.

Although the invention has been described with reference to thesuperimposition of a simple harmonic motion and that of an intermittentmotion device, the smooth action with minimum shock and vibration canalso be obtained by other combinations of motion, for example, aconstant-acceleration motion having minimum acceleration at the midpointthereof superimposed on the intermittent motion of a Geneva gear.

FIGS. 6-10 schematically illustrate the alternate actuation of indexingplates 92 and 95 and the inherent mechanical interlocking thereof. Inorder to more clearly illustrate the cam track, the shaft 28 and sleeve55 are illustrated as extending in opposite directions in FIGS. 6-10,whereas in the preferred embodiment the sleeve 55 surrounds the shaft28. FIG. 6 shows the conditions prior to the first step of Geneva gear123 wherein the rotatable contacts 29 and 56 are still in engagementwith stationary contacts 12, the midportion MP7 of the camming surfacemeans 105 of the cylindrical cam 99 is disposed between a pair ofadjacent cam followers 93A and 93B of index plate 92 and is alsodisposed between a pair of adjacent cam followers %A and Q63 on indexplate 95. Consequently the index plates 92 and 95 are locked againstrotation and the rotatable contacts 29 and 56 cannot open. FIG. 7 showsthat after the first sixty degree step of Geneva gear 123, cam follower93B of index plate 92 is in positive engagement with the double-edge camtrack portion 117 and the movable contact 29 has been displaced slightlyon stationary contact 12 but is still in engagement therewith. Camfollowers 96A and 96B are still disposed on opposite sides ofrnidportion 167 which does not advance axially as cam 99 is rotated, andconsequently movable contact 55 is still locked at rest. FIG. 8illustrates the condition midway through the second step of cam 99 afterthirty degree further rotation of Geneva gear 123 wherein the rotatablecontact 29 is disengaged from one stationary contact 12 and is midwaybetween adjacent stationary contacts 12, cam follower 93B is midwaythrough the steeper-slope portion of the double-edge cam track 117 andpositively held therein, and cam follower 93A is out of engagement withthe carnming surface means ltlfi. At the end of the second step afterthirty degree further rotation of Geneva gear 123 as shown in FIG. 9,the rotatable contact 29 is in engagement with a succeeding stationarycontact 12 and cam follower 9313 has passed through the steeper-slopeportion of, but is still in engagement with the double-edge cam trackpor tion 117, and a succeeding cam follower 93C of index plate 92 isready to come into engagement with the camming surface means Hi5. Afterthe third step of Geneva gear 123 as shown in FIG. 10, the rotatablecontact 29 has been displaced into its final position at rest onsucceeding stationary contact 12; cam follower 93B has been disengagedfrom the double-edge cam track portion 117; and cam followers @313 and93C are disposed on opposite sides of rnidportion 167, thus locking (theindex plate 92 against rotation and positively holding the rotata blecontact 29 at rest. It will be noted in FIGS. 6-10 (that during thethree operating steps of Geneva gear 123, the index plate 95 is lockedagainst rotation by the midportion 107 which throughout the three stepsis disposed between the cam followers 96A and 96B, thereby holding themovable contact 56 at rest. At the end of the three steps of Geneva gear123, the cam follower 96B is disposed in a position relative to thedouble-edge cam track portion 117 identical to that of cam follower 9313prior to the first step. Consequently the next three steps of Genevagear 123 will peripherally displace cam follower %B to rotate plate 95and index the movable contact 56 between stationary contacts. Thedirect-drive means including cylindrical cam 99 and index plates 92 and95 is thus capable of positively and nonresilientily indexing one of themovable contacts 29 or 56 at a controlled speed while concurrentlyholding the other rotatable contact at rest, of locking both rotatablecontacts 29 and 56 at rest simultaneously and alternately driving theindex plates 92 and 95 to alternately index the rotatable contacts 29and 56 between stationary contacts 12.

Although only a single preferred embodiment of the invention has beenillustrated and described, many modircations and variations thereof willbe apparent to those skilled in the art, and therefore it is intended inthe appended claims to cover all such modifications and variations asfall within the true spirit and scope of the invention.

I claim:

1. An electrical tap changing under load mechanism comprising, incombination, a plurality of arcuately arranged stationary contacts, amovable contact for sequentially engaging said stationary contacts, andintermittent motion transmitting means including a pair of l itrelatively movable members the first of which is positively andnonresiliently connected to said movable contact and the second of whichdrives said first member for indexing said movable contact withaccelerated motion from one stationary contact to a succeedingstationary contact, said movable con-tact interrupting current underload when it is disengaged from said one stationary contact andcompeting an electrical circuit under load when it engages saidsucceeding stationary contact, one of said members having a single meansin continuous positive engagement with the other of said members bothduring actuation of said movable contact and while said movable contactis at rest and said second member positively driving and directlycontrolling the speed of sid movable contact at all times while it isbeing indexed between said stationary contacts, whereby contact bounceis avoided.

2. An electrical tap changing under load mechanism comprising, incombination, at least three arcuately arranged stationary contactsconnected to taps of an elec trical Winding, a movable contact forsequentially engaging said stationary contacts, and means including apair of members the first of which is positively and nonresilientlyconnected to said movable contact and the second of which drives saidfirst member for indexing said movable contact from one stationarycontact to a succeeding stationary contact, said movable contactinterrupting current under load in the electrical circuit to one of saidtaps when it is disengaged from said one stationary contact andcompleting an electrical circuit under load to an adjacent tap when itengages said succeeding stationary contact,

one of said members having a single cam track means in continuouspositive engagement with the other of said members both during actuationof said movable contact and while said movable contact is at rest, saidsecond member positively driving and directly controlling the speed ofsaid movable contact at all times while it is being indexed between saidstationary contacts and decelerating said movable contact to a fractionof its maximum velocity before said movable contact engages saidsucceeding stationary contact and also decelerating said movable contactto a final position at rest in engagement with said succeedingstationary conact, said one member being in continuous positiveengagement with the other of said members during said deceleration,whereby contact bounce of said movable contact is eliminated.

3. An electrical ltap changing under load mechanism comprising, incombination, at least three stationary contacts arranged in an arcuatepath, a movable contact adapted to sequentially engage said stationarycontacts, and means including a rotatable member carrying cam followermeans disposed away from the axis thereof and being positively andnonresiliently connected to said movable contact for indexing saidmovable contact with accelerated motion from one stationary contact to asucceeding stationary contact, said movable contact interrupting currentunder load when it is disengage-d from said one stationary contact, saidmeans for indexing also including an intermittent motion transmittingdevice characterized by gradual acceleration and retardation at the endsof the motion and rapidly accelerated and decelerated motiontherebetween and a positive-motion cam in continuous engagement withsaid cam follower means and positively driving and directly controllingthe velocity of said movable contact at all times while it is beingindexed between said stationary contacts, the motion transmitted by saidcam being characterized by gradual change of velocity in the vicinity ofthe maximum velocity and the motion of said cam being superimposed uponthat of said intermittent device and producing smooth action of saidmovable contact, said indexing means starting said movable contactslowly and accelerating it to a substantial portion of its maximumvelocity before it is disengaged from said onestationary Contact.

4. An electrical tap changing under load mechanism comprising, incombination, at least three stationary contacts arranged in an arcuatepath and connected to taps of an electrical winding, a movable contactadapted to sequentially engage said stationary contacts, and meansincluding a rotatable member carrying cam follower means disposed awayfrom the axis thereof and being positively and nonresiliently connectedto said movable contact for indexing said movable contact from onestationary contact to a succeeding stationary contact, said movablecontact interrupting current under load in the electrical circuit to oneof said taps when it is disengaged from said one stationary contact andcompleting an elec trical circuit under load to an adjacent ttap when itengages said succeeding stationary contact, said means for indexing alsoincluding an intermittent motion transmitting device characterized byrelatively gradual acceleration and retardation adjacent the ends of themotion and rapidly accelerated and decelerated motion intermediate saidends and a simple harmonic positive-motion cam in continuous engagementwith said cam follower means and being rotatably driven in three sixtydegree steps by said intermittent device to index said movable contactbetween said stationary contacts, said cam follower means during thefirst step being displaced to the beginning of the steeper slope portionof said simple harmonic motion cam and the opening and reclosing of saidcontacts occurring during the second step of sixty degrees of simpleharmonic motion transmitted by said cam, the motion of said intermittentdevice being superimposed on that of said cam and effecting smoothaction of said rotatable contact during said indexing.

5. An electrical tap changing under load mechanism comprising, incombination at least three arcuately arranged stationary contacts, amovable contact adapted to sequentially engage said stationary contacts,and means including a pair of rotatable members the first of which ispositively and nonresiiientl connected to said movable contact and thesecond of which displaces said first memher in a peripheral directionfor indexing said movable contact with rapidly accelerated motion fromone stationary contact to a succeeding stationary contact, said movablecontact interrupting current under load when it is disengaged from saidone stationary contact and completing an electrical circuit under loadwhen it engages said succeeding stationary contact, one of said membershaving a single means in continuous positive engagement with the otherof said members both during indexing of said movable contact and whilesaid movable contact is at rest and said second member positivelydriving and directly controlling the velocity of said movable contact atall times while it is being indexed between said stationary contacts,the midportion of the velocity-time curve of the motion transmitted bysaid indexing means to said movable contact being approximatelysinusoidal with maximum velocity occurring during said midportion, saidindexing means gradually accelerating and gradually decelerating saidmovable cont act at the initial and final portions of said motion andchanging the velocity of said movable contact gradually adjacent themaximum velocity point of said midportion of said velocity-timechanacteristic.

6. An electrical tap changing under load mechanism comprising, incombination, at least three arcuately arranged stationary contacts, amovable contact for sequentially engaging said stationary contacts, andmeans for indexing said movable contact from one stationary contact to asucceeding stationary contact, said movable contact interrupting currentunder load when it is disengaged from said one stationary contact, saidmeans including a prime mover, an intermitent motion transmitting deviceoperatively driven by said prime mover, said intermittent motion devicebeing characterized by gradual acceleration and retardation at the endsof the motion and rapid acceleration and deceleration in the midportionthereof, and a simple harmonic motion transmit-ting device between saidintermittent motion device and said movable contact, said simpleharmonic motion device positively driving and directly controlling thespeed of said movable contact at all times as it is indexed between saidstationary contacts, whereby said prime mover may start without load andgradually accelerating and gradually decelerating motion is imparted tosaid movable contact at the ends of said indexing and the velocity ofsaid movable contact is changed gradually as the velocitytimecharacteristic of said movable contact changes from a positive to anegative slope.

7. An electrical tap changing under load mechanism comprising, incombination, at least three arcuately arranged stationary contactsconnected to taps of an electrical winding, a movable contact forsequentially engaging said stationary contacts, and means for indexingsaid movable contact from one stationary contact to a succeedingstationary contact, said movable contact interrupting current under loadin the electrical circuit to one of said taps when it is disengaged fromsaid one stationary contact and completing an electrical circuit underload to an adjacent tap when it engages said succeeding stationarycontact, said means including a prime mover, an intermittent motionGeneva gear operatively driven by said prime mover, and a motiontransmitting device having the chanacteristic of gradual change ofvelocity with time at the midpontion of the velocity-time characteristicthereof disposed between said Geneva gear and said movable contact, thesuperimposition of said Geneva gear and said device providing smoothaction of said movable contact with minimum vibration and shock eflects.

8. An electrical tap changing under load mechanism comprising, incombination, a plurality of arcuately arranged stationary contacts, apair of individually operable movable contacts for sequentially engagingsaid stationary contacts, means for alternately indexing said movablecontacts from one stationary contact to a succeeding stationary contactincluding first and seond rotatable members positively andnonresiliently connected to individual ones of said movable contacts,each said movable contact interrupting current under load when it isdisengaged from one stationary contact and completing an electricalcircuit under load when it engages said succeeding stationary contact,and a motion transmitting member simultaneously continuously directlyengaging said first and second members both during indexing and at restand when operated alternately displacing said first and second membersto actuate said movable contacts with accelerated motion and said motiontransmitting member positively driving and directly controlling thevelocity of said movable contacts at all times as they are indexedbetween said stationary contacts.

9. An electrical tap charging under load mechanism comprising, incombination, a plurality of circumferentially disposed stationarycontacts, a pair of individually operable movable contacts adapted tosequentially engage said stationary contacts, a shaft carrying one ofsaid movable contacts, a sleeve rotatably surrounding said shaft andcarrying the other of said movable contacts, means for alternatelyindexing said movable contacts between said stationary contactsincluding first and second rotatable members one of which is in positiveand nonresilient connection with said shaft and the other of which is inpositive and nonresilient connection with said sleeve, and a rotatablemotion transmitting member in continuous positive engagement with saidfirst and second rotatable members and being adapted to alternatelyrotatably drive said first and second members to alternately index saidmovable contacts from one stationary contact to a succeeding stationarycontact, each said movable contact interrupting current under load whenit is disengaged from said one stationary contact and completing anelectrical circuit under load when it engages said succeeding stationarycontact.

10. A tap changing under load mechanism comprising, in combination, atleast three circumferentially disposed id stationary contacts connectedto taps of an electrical winding, a movable contact operative tosequentially engage said stationary contacts, and means for indexingsaid movable contact from one stationary contact to a succeedingstationary contact including an index plate positively andnonresiliently connected to said movable contact and having a pluralityof circumferentially spaced apart cam followers and a cam adapted tosequentially engage and displace said cam followers to rotate said indexplate and being in positive engagement with at least one of said camfollowers at all times and positively driving and directly controllingthe velocity of said movable contact at all times as it is indexedbetween said stationary contacts, said movable contact interruptingcurrent under load in the electrical circuit to one of said taps when itis disengaged from said one stationary contact and completing anelectrical circuit under load to an ad acent tap when it engages saidsucceeding stationary contact.

11. A tap changing under load mechanism comprising, in combination, aplurality of circumferentially disposed stationary contacts, a pair ofindividually operable rotatable contacts adapted to sequentially engagesaid stationary contacts, a first indexing plate positively andnonresiliently connected to one of said rotatable contacts, a secondindexing plate spaced from and coaxial w th said first indexing plateand positively and nonresiliently connected to the other rotatablecontact, a plurality of oncumferentially spaced apart cam followers oneach of said indexing plates, and a positive-motion cam disposed betweensaid indexing plates successively engaging and displacing said camfollowers on each of said plates and indexing said rotatable contactsbetween said stationary contacts each said rotatable contactinterrupting current under load when it is disengaged from one of saidstationary contacts and completing an electrical circuit under load whenit engages a succeeding stationary contact, said cam alternatelyengaging and displacing a cam follower on said first indexing plate anda cam follower on said second indexing plate and positively engaging atleast one of said cam followers on both of said plates at all times,whereby motion of said cam is directly transmitted to said rotatablecontacts and said cam locks said rotatable contacts at rest.

12. In a tap changing under load mechanism, the combination with atleast three circumferentially disposed stationary contacts connected totaps of an electrical winding and a rotatable contact for sequentiallyengaging said stationary contacts, of means for indexing said rotatablecontact between said stationary contacts including a rotatable indexplate positively and nonresiliently connected to said rotatable contactand carrying a plurality of circumferentially spaced apart cam followersand a cylindrical cam disposed adjacent said index plate and havingcamming surface means thereon a portion of which is in a planesubstantially perpendicular to the axis of said cam and at least one endof said camming surface means diverging from said plane, said cammingsurface means sequentially engaging and displacing the cam followers ofsaid index plate when said cylindrical cam is actuated to actuate saidindex plate, said camming surface means positively engaging at least oneof said cam followers at all times, whereby said cam indexes saidrotatable contact between stationary contacts and also locks saidrotatable contact at rest, said rotatable contact interrupting currentunder load in the electrical circuit to one of said taps when it isdisengaged from one of said stationary contacts and completing anelectrical circuit under load when it engages a succeeding stationarycontact.

13. in a tap changing under load mechanism, the combination with aplurality of circumferentially disposed stationary contacts and a pairof rotatable contacts individually operable to sequentially engage saidstationary contacts; of a pair of rotatable, axially spacedapart,coaxial index plates each having a plurality of circumferentially spacedapart cam followers and being positively and nonresiliently connected toone of said rotatable contacts, and a cylindrical cam disposed betweensaid index plates having camming surface means thereon the end portionsof which diverge axially relative to said cam, one of said diverging endportions sequentially engaging said cam followers on each of said platesand alternately engaging and displacing said cam followers on said pairof plates when said cam is rotated in the forward direction and theother said diverging end portions doing so when said cam is rotated inthe reverse direction, the portion of said camming surface means betweensaid end portions being in positive engagement with the cam followers ofone of said index plates while a cam follower of the other of said indexplates is being displaced by one of said end portions, each saidrotatable contact interrupting current under load when it is disengagedfrom one stationary contact and completing an electrical circuit underload when it engages a succeeding stationary contact.

14. In a tap changing under load mechanism, the combination with aplurality of circumferentially disposed stationary contacts and a pairof coaxial, spaced apart, individually operable rotatable contacts forsequentially engaging said stationary contacts; of a rotatable shaftcarrying one of said rotatable contacts and a sleeve rotatablysurrounding said shaft and carrying the other of said rotatablecontacts, a pair of rotatable, axially spaced apart, coaxial indexplates each carrying a plurality of circumferentially spaced apart camfollowers, one of said plates being positively and nonresilientlyconnected to said shaft and the other of said plates being positivelyand nonresiliently connected to said sleeve, and a cylindrical camdisposed between said plates with its axis substantially at right anglesto the axis thereof and having camming surface means adapted tosequentially engage the cam followers of each of said index plates andto alternately engage and displace said cam followers of said pair ofplates to index said rotatable contacts alternately between saidstationary contacts, each said rotatable contact interrupting currentunder load when it is disengaged from one of said stationary contactsand completing an electrical circuit under load when it engages asucceeding stationary contact.

15. A tap changing under load mechanism comprising, in combination, aplurality of circumferentially disposed stationary contacts, a pair ofcoaxial, axially spaced apart, rotatable contacts, a shaft carrying oneof said rotatable cont cts, a sleeve rotatably surrounding said shaftand carrying the other of said rotatable contacts, a pair of coaxial,axially spaced apart, rotatable index plates each having a plurality ofcircumferentially spaced apart cam followers, one of said plates beingpositively and nonresiliently connected to said shaft and the other ofsaid plates being positively and nonrcsiliently connected to saidsleeve, and a cylindrical cam disposed between said index and having araised carnrning surface thereon extending circumferentially more than360 degrees around the periphery of said cam, a midportion of saidcamming surface being in a plane substantially perpendicular to the axisof said cam and the end portions of said camming surface diverging fromsaid plane axially relative to said cam axis and when said cam isrotated sequentially engaging and peripherally displacing the camfollowers on each of said plates and alternately engaging andperipherally displacing the cam followers on said pair of plates toindex said rotatable contacts alternately between said sta tionarycontacts, each said rotatable contact interrupting current under loadwhen it is disengaged from one of said stationary contacts andcompleting an electrical circuit under load when it engages a succeedingstationary contact, said midportion being disposed between andpositively engaging an adjacent pair of said cam followers of one ofsaid index plates when a cam follower of the other of said index platesis in engagement with said end portions, whereby one of said indexplates is positively held by said midportion to lock one of said movableconi6 tacts at rest while the other of said index plates is beingrotated by said end portions to index the other of said rotatablecontacts between stationary contacts.

16. A tap changing under load mechanism, comprising, in combination, aplurality of circumferentially disposed stationary contacts a pair ofindividually operable rotatable contacts adapted to sequentially engagesaid stationary contacts, a pair of rotatable index plates positivelyand nonresiliently connected to individual ones of said rotatablecontacts and each carrying a plurality of circumferentially spaced apartcam followers, and a positivemotion cam having camining surface meansfor sequentially engaging said cam followers of each said index plateand for alternately eng-ging and peripherally displacing said camfollowers of said pair of index plates, said camining surface means whensaid cam is rotated transmitting motion to one of said cam followers ina series of steps in the first ofwhich said carnrning surface meanspositively engages said one cam follower and displaces it to thebeginning of the portion of said camming surface'having the steeperslope and which is most advantageous for rapid acceleration of therotatable contact associated therewith during the succeeding step and inthe second of which said one cam follower is peripherally displacedalong said steeper slope portion of said caniming surface to index saidrotatable contact from one stationary contact into engagement with asucceeding stationary contact, said cam accelerating said rotatablecontact to maximum velocity between said stationary contacts and theslope of said steeper portion changing gradually in the vicinity of saidmaximum velocity, each said rotatable contact interrupting current underload when it is disengaged from said one stationary contact, said campositively constraining said one cam follower during all of said stepsand concurrently positively constraining said cam followers of saidother index plate during all of said steps, and a Geneva gear, saidGeneva gear transmitting motion with relatively low acceleration andretardation adjacent the initial and final portions of the motion, thesuperimposition of the motion of said cam on the motion of said Genevagear providing smooth action of said rotatable contact with minimumvibration and shock.

17. In a tap changing mechanism in accordance with claim 16 whereinduring said second step said cam is adapted to accelerate said rotatablecontact to a substantial portion of its maximum velocity before it isdisenfrom said one stationary contact and to decelerate said rotatablecontact to a fraction of its maximum velocity before it engages saidsucceeding stationary contact and to positively constrain said one camfollower during said deceleration,whereby contact bounce of saidrotatable Contact is eliminated.

18. A tap changing under load mechanism comprising, in combination, atleast three circumferentially disposed stationary contacts connected totaps of an electrical winding, a rotatable contact adapted tosequentially ensaid stationary contacts, a rotatable member posi tivelyand nonresiliently connected to said rotatable contact and carrying aplurality of circumferentially spaced apart cam followers disposed awayfrom the axis thereof, and a positive-motion cam having an approximately8- shaped cam track adapted when said cam is rotated to sequentiallyengage said cam followers and to transmit motion to each said camfollower in a series of steps in the first of which said cam trackpositively engages said cam follower and displaces it to a position atthe beginning of the steeper portion of said cam track wherein said camfollower is in the most advantageous position to rapidly accelerate saidcontact during the succeeding step and in the second of which said camfollower is peripherally displaced by said steeper portion to index saidrotatable contact from one stationary contact into engagement with asucceeding stationary contact, said rotatable contact interruptingcurrent under load in the electrical circuit to one of said taps when itis disengaged from said one stationary contact and completing anelectrical circuit under load to an adjacent tap when it engages saidsucceeding stationary contact, said cam track positively constrainingsaid cam follower during said series of steps and said positive motioncam positively driving and directly controlling the velocity of saidrotatable contact at all times as it is indexed between said stationarycontacts.

19. An electrical tap changing under load mechanism comprising, incombination, at least three circumferentially disposed stationarycontacts, first and second individually operable rotatable contactsadapted to sequentially engage said stationary contacts, and indexingmeans including a positive-motion cam for alternately indexing saidfirst and second rotatable contacts from one stationary contact to asucceeding stationary contact so that said rotatable contacts arerapidly accelerated to a substantial portion of their maximum velocitybefore they disengage said one stationary contact and are retarded to afraction of said maximum velocity before they engage said succeedingstationary contact, each said rotatable contact interrupting currentunder load when it is disengaged from said one stationary contact andcompleting an electrical circuit under load when it engages saidsucceeding stationary contact, said positive-motion cam positivelydriving one of said rotatable contacts and positively controlling itsspeed at all times as it is indexed between said stationary contacts andlocking the other rotatable contact at rest while indexing said onerotatable contact.

20. In a tap changing under load mechanism, the combination of at leastthree arcuately arranged stationary contacts connected to taps of anelectrical winding, a movable contact adapted to sequentially engagesaid stationary contacts, and indexing means including a positive motioncam and cam follower means connected to said movable contact and drivenby said cam for initially wiping said movable contact at relatively lowvelocity along one stationary contact and for accelerating said movablecontact to a substantial portion of its maximum velocity before itdisengages said one stationary contact and for decelerating said movablecontact to a fraction of its maximum velocity before it engages asucceeding stationary contact, said movable contact interrupting currentunder load in the electrical circuit to one of said taps when it isdisengaged from said one stationary contact and completing an electricalcircuit under load to an adjacent tap when it engages said succeedingstationary contact, said indexing means wiping said movable contactalong said succeeding stationary contact at relatively low velocity intoits final position with said succeeding contact and said cam positivelydriving and directly controlling the velocity of said movable contact atall times as it is indexed from said one stationary contact to saidsucceeding stationary contact, whereby bounce of said movable con- 18tact relative to said succeeding stationary contact is eliminated andarcing therebetween is reduced.

21. In a tap changing under load mechanism, in combination, a pluralityof circumferentially disposed stationary contacts, a rotatable contactfor sequentially engaging said stationary contacts, intermittent motiontransmitting means including a pair of members the first of which ispositively and non-resiliently connected to said rotatable contact andthe second of which rotatably drives said first member for indexing saidrotatable contact from one stationary contact to a succeeding stationarycontact so that it is initially accelerated gradually and thenaccelerated rapidly to a substantial portion of its maximum velocitybefore it is disengaged from said one stationary contact, said movablecontact interrupting current under load when it is disengaged from saidone stationary contact and completing an electrical circuit under loadwhen it engages said succeeding stationary contact, said means forindexing including means for changing the velocity of said rotatablecontact relatively gradually in the vicinity of the maximum velocitypoint on its time-velocity characteristic, one of said members having asingle means in continuous positive engagement with the other of saidmembers both during indexing of said rotatable contact and while saidrotatable contact is at rest and said second member positively drivingand directly controlling the velocity of said rotatable contact at alltimes during the indexing thereof between stationary contacts anddecelerating said rotatable contact to a fraction of its maximumvelocity before it engages said succeeding stationary contact.

References Cited in the file of this patent UNITED STATES PATENTS1,764,319 Kurda June 17, 1930 1,863,392 Brand June 14, 1932 1,867,147Haller July 12, 1932 2,253,654 Schroder Aug. 16, 1941 2,363,886 McKenneyNov. 28, 1944 2,395,803 Bruckner et al Mar. 5, 1946 2,480,589 McKenneyAug. 30, 1949 2,785,242 V/hite Mar. 12, 1957 2,791,648 Maloney May 7,1957 2,878,333 McCarty et al Mar. 17, 1959 FOREIGN PATENTS 850,924France Dec. 29, 1939 893,924 Germany Oct. 12, 1953 29,235 Great BritainOct. 22, 1898 of 1897 583,365 Great Britain Dec. 17, 1946 106,119 SwedenDec. 15, 1946 209,052 Switzerland Mar. 15, 1940

1. AN ELECTRICAL TAP CHANGING UNDER LOAD MECHANISM COMPRISING, INCOMBINATION, A PLURALITY OF ARCUATELY ARRANGED STATIONARY CONTACTS, AMOVABLE CONTACT FOR SECQUENTIALLY ENGAGING SAID STATIONARY CONTACTS, ANDINTERMITTENT MOTION TRANSMITTING MEANS INCLUDING A PAIR OF RELATIVELYMOVABLE MEMBERS THE FIRST OF WHICH IS POSITIVELY AND NONRESILIENTLYCONNECTED TO SAID MOVABLE CONTACT AND THE SECOND OF WHICH DRIVES SAIDFIRST MEMBER FOR INDEXING SAID MOVABLE CONTACT WITH ACCELERATED MOTIONFROM ONE STATIONARY CONTACT TO A SUCCEEDING STATIONARY CONTACT, SAIDMOVABLE CONTACT INTERRUPTING CURRENT UNDER LOAD WHEN IT IS DISENGAGEDFROM SAID ONE STATIONARY CONTACT AND COMPETING AN ELECTRICAL CIRCUITUNDER LOAD WHEN IT ENGAGES SAID SUCCEEDING STATIONARY CONTACT, ONE OFSAID MEMBERS HAVING A SINGLE MEANS IN CONTINUOUS POSITIVE ENGAGEMENTWITH THE OTHER OF SAID MEMBERS BOTH DURING ACTUATION OF SAID MOVABLECONTACT AND WHILE SAID MOVABLE CONTACT IS AT REST AND SAID SECOND MEMBERPOSITIVELY DRIVING AND DIRECTLY CONTROLLING THE SPEED OF SID MOVABLECONTACT AT ALL TIMES WHILE IT IS BEING INDEXED BETWEEN SAID STATIONARYCONTACTS, WHEREBY CONTACT BOUNCE IS AVOIDED.